The present invention relates generally to hand-held calculators and more particularly to a hand-held demonstration calculator for classroom use and the like.
Generally the only devices available for facilitating classroom instruction in the operation of a calculator are calculators having very large displays themselves or providing a simulated display which produces an output, display that only remotely resembles the display actually seen on the conventional hand-held calculator. In addition to producing displays which are typically not well-suited for group viewing, these devices are typically of such high cost that their universal use is impractical.
U.S. Pat. No. 4,154,007 discloses a hand held calculator having a liquid crystal display supported on a transparent substrate so that portions of the LCD that are excited obstruct light passage while the remainder of the display is transparent--i.e., able to transmit light therethrough so as to enable projection of an enlarged image of the display onto a projection screen. While this device enables students to follow the results of the various keyboard operations performed by the instructor, it does not permit the students to see the actual keyboard manipulations themselves as they are performed by the instructor. In other words, the students see output only, not input, and thus cannot "put together" the manual and visual operations as necessary to acquire calculator proficiency. While this is a significant defect with respect to the data entry or integer keys, it is an even more serious defect with respect to the operation instruction keys which dictate how the calculator will act on the data entered. While the results of the data entry key activities are immediately reflected in the display and easily relatable on a logical basis to data entry key activity, the operation instruction key activities are typically not indicated in the display and can be quite difficult to discern simply from the changes in the display (for example, the effect of actuating a square root key on a lengthy decimal number). While in a simple, small calculator the operation instruction keys may be few, in larger, more complex (but still hand-held) calculators and especially in programmable calculators the number of operation instruction keys may far outnumber the number of data entry keys, and the students may require extensive training in the use thereof.
Accordingly, it is an object of the present invention to provide a calculator adapted so that both the output thereof and the input thereto on the operation instruction keys can be readily projected for group viewing by use of equipment freguently available in most classroom environments.
A further object is to provide such a calculator adapted to enable both the output display and the keyboard input thereto to be so projected.
A further object is to provide such a calculator which enables students to observe all keyboard input to and display output from the calculator.
It is also an object of the present invention to provide such a calculator which is inexpensive to produce, easy to operate, and of rugged construction.